1919] Coit— Hodgson : Abnormal Shedding of Washington Navel Orange 289 



ening tissue at the base of the ovary may prevent the fall of the fruit. 

 These dead, dry fruits, as shown in plate 31, arc often quite conspicuous 

 on the trees. Soon after the application of the stimulus, but several 

 days before actual separation, the larger fruits assume a characteristic 

 appearance, losing their luster and taking on a lighter green color. In 

 the case of exposed fruits the yellow color is deeper around the apex, but 

 this is not the case with shaded fruits. It is thus a simple matter to 

 select any number of fruits which are destined to absciss several days 

 before separation actually occurs. 



Experiments carried on in the laboratory and observations made in 

 the field, both in a survey of the citrus districts of southern California 

 immediately following the heat wave of June 15-17, 1917. and at 

 Bakersfield during 1916 and 1917, have shown that the time inter- 

 vening between the application of the stimulus and actual separation 

 is from four to ten days. The shorter periods were obtained in the 

 laboratory, where the room temperature was uniformly high. Our 

 observations are that under field conditions abscission is ordinarily 

 complete within five to eight days after the application of the stimulus. 



Normally, orange blossoms, being borne in cymes, open in succession, 

 beginning about March 20 in the San Joaquin Valley and continuing 

 about one month. Abscission varies with the season but usually it is 

 in evidence from April 1 to about July 1, a period of three months. 

 The period of maximum shedding occurs during the latter half of 

 April. It should be noted that the season of 1917 was unique in being 

 the latest on record. Protracted cool weather delayed the bloom fully 

 five weeks, with a consequent delay of the period of maximum shedding. 

 A comparison of the mean maximum atmospheric temperatures for the 

 years 1914-17 inclusive is shown in table 2. The comparative lateness 

 of the 1917 season is apparent from a study of this table. 



TABLE 2 



Monthly Mean Maximum Temperatures for Ten Months at Bakersfield 

 Compiled from U. S. Weather Bureau Records 



